Long-Term Night Shifts Linked to Increased Breast Cancer Risk

Female night workers are at higher risk of developing breast cancer than other women, researchers have found.

According to the findings of a new study, women who work night shifts for more than 30 years are twice more likely to develop breast cancer as compared to women who worked night shifts for 29 or fewer years.

The study
For the purpose of the study, researchers from the Queen’s University in Canada looked at career history of over 2,300 female workers. While 1,134 women were diagnosed with breast cancer, 1,179 women were without the disease.

A third of the participants in both groups were night shift workers. The participants’ night shift was divided into three categories – 14 or fewer years of night shift, 15 to 29 years of night shift and 30 or more years of night shift.

No association between working night shift and increased breast cancer risk was found among women who worked for 14 or fewer years of night shift or 15 to 29 years of night shift.

But women who worked night shifts for 30 or more years were twice more likely to develop breast cancer compared to peers who worked night shifts for 29 or fewer years, researchers highlighted.
Although various previous studies have purported the link between working night shift and increased breast cancer risk the association is still less than clear, researchers noted.

Long-term exposure to artificial lighting is known to suppress the production of melatonin, the body hormone responsible for inducing sleep.

Impaired melatonin production in turn leads to increased production of estrogen in the body, triggering breast cancer in some women.

“While light at night and melatonin have been proposed as one pathway through which night shift work may influence breast cancer, and data from prospective studies has generally supported a protective effect of melatonin on breast cancer

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